Republican voters in the U.S. state of Iowa will hold party caucuses Tuesday in the first step in choosing a candidate that will challenge President Barack Obama in the November election.

Voters will gather in churches, school houses and other meeting places to cast their vote.

The latest voter surveys indicate that former Massachusetts governor Mitt Romney has the lead in Iowa among Republican contenders.

Romney is closely followed by Texas Congressman Ron Paul. Former Pennsylvania senator Rick Santorum is in third place.

After days of criticizing each other, the Republican candidates on Monday focused on President Obama, a Democrat.

Romney hammered away at Mr. Obama's record on the economy.

“He said if 'I can't get this economy turned around in 3 years, I'm looking at a one-term proposition.' I'm here to collect.”

Santorum attacked the Obama administration for regulations on business.

“People are saying, well what's hurting this economy? This president, and his top down, I know best, I'm going to tell you how to run your business, how to run your farm, how to run your life. The huge cost that that's putting on the American people and business is crushing this economy.”

Former congressman Newt Gingrich, who is well behind the leaders in the poll, also took aim at Mr. Obama, blaming him for the political divisions in Washington.

“What America needs is a president who thinks about the children and the grandchildren of this country and the future of this country, and puts that above his own petty, arrogant ambitions and instead serves the country.”

Voters in Iowa often do not crown the eventual presidential nominees for either Republicans or Democrats. But its first-in-the-nation caucuses can serve as a launchpad for political success in other states during the next several weeks of the candidate selection process. The Iowa caucuses also serve to push weaker contenders out of the race.

A survey Monday in Iowa's largest newspaper, the Des Moines Register, indicates 41 percent of voters had not made up their minds.

Of the seven Republican contenders, one of them, the former U.S. ambassador to China Jon Huntsman, has not campaigned in Iowa. He is pinning his hopes on a good showing in the northeastern state of New Hampshire, where voters will cast primary election ballots on January 10.

Mr. Obama is unopposed for his party's renomination, but he faces a difficult test to win another term. The nation's economy, the world's largest, has recovered sluggishly from the 2007-2009 recession, leaving many voters questioning his leadership.